1. Field of the Invention
This invention relates to a multi-chambered apparatus for scrubbing gravels and substances containing heavy precious metals.
2. Description of the Prior Art
The use of scrubbing units for the purpose of washing and breaking up various materials is known to those of skill in the art. For example, it is known to use scrubbers to wash and liberate the rocks derived from compacted gravel deposits. When scrubbers are used for the extraction of heavy metal they are most frequently combined with a rotating screen or trommel as part of the same unit. Combining the rotating screen with the scrubber as part of the same unit has been done in the past. This invention proves that such a combination is less efficient than running the scrubber and screening units separately and at separate speeds.
There are a variety of devices known in the prior art that will accomplish the function of washing and liberating rocks, clay-bound precious metals and similar materials. Non-rotating devices such as vibrating grizzlys have been used to break up large chunks of uranium ore. Rotating scrubbers are also known in the prior art but their internal structure is almost exclusively circular. Circular scrubbers have been found to be ineffective for the purpose of separating heavy precious metals such as gold from a clay or clay-like matrix. The circular nature of the vast majority of circular type scrubbers is such that the gold bearing clay and gravel merely slides up and down the walls of the rotating apparatus and accordingly very little of the precious metal is separated therefrom. The prior art appears to lack a mechanism which will effectively disintegrate and scrub the gravel and disintegrate the clay and put it into solution, leaving the heavy precious metals behind. In order to overcome some of the disadvantages of the prior art, it was known to add agitator baffles or lifters to the interior of a circular type scrubber. While agitating blades often resulted in greater amounts of clay being dissolved, they were found to be inefficient and also tended to break up the particles of heavy precious metal into smaller pieces thereby making them more difficult to recover.
Part of the present invention comprises the discovery that a scrubber having a polygonal interior produces a superior disintegrating scrubbing and washing action to that obtained by prior art circular type scrubbers. In the circular type of prior art scrubbers the material merely slides around the inside of the apparatus. According to the present invention the materials are churned in such a fashion as to throw the clay or gravel up against the sides of the scrubbing unit. By varying the speed and inclination of the scrubber it is possible to obtain the optimum separation of precious metals from a gravel or clay-like matrix without significant deterioration of the metal particles.
The prior art appears to disclose only two references to scrubber type devices having a polygonal interior. For example, Vanduzen, U.S. Pat. No. 292,075 discloses a "Rumble for Scouring Casings, Washing Ores, etc.", wherein the cylinder is "of polygonal or angular form . . . in this instance an octagon". It was further noted that the Vanduzen reference discloses that the device is adapted for use with "precious metals" but it is not clear whether the Vanduzen reference contemplated the use of such a device in the context of precious metal bearing placer material composed of clays or gravels. In addition, the Vanduzen reference also appears to teach the use of "heavy balls" in order to improve the action of the rumble and further discloses the technique of grinding in the context of washing in that a tub is provided in which the polygonal cylinder revolves.
Harris, U.S. Pat. No. 3,730,442 is also noted in that it discloses a grinding apparatus having an octagonal shape.
Smith, U.S. Pat. Nos. 764,870, 894,174 and Jain, U.S. Pat. No. 2,137,051 all disclose gold and silver agitators of the sort associated with cyanide gold extraction process. Those references appear to be relevant only insofar as they disclose the desirability of agitation in processes directed toward the extraction of gold.
Moore, U.S. Pat. No. 706,334 is of general interest in that it discloses an apparatus for leaching ores which provides for the use of grinding balls in a manner generally known to those of skill in the art.
While the prior art does appear to include two disclosures directed toward scrubber type devices having a polygonal cross-section, such devices are not known to have been used, nor has their value been recognized for use on precious metals found in placer materials containing gravel or clay or clay-like matrix. Moreover, the polygonal type scrubbers disclosed by the prior art appear to be very crude and inefficient for the purpose of assisting in the removal of heavy precious metal. It was in the context of these and other disadvantages of the prior art that the present invention arose.